Brachytherapy is a type of radiation therapy used to treat malignant tumors such as cancer of the breast or prostate. In general, brachytherapy involves positioning a radiation source directly into target tissue, which may typically include the tumor and/or surrounding tissue that may contain potentially cancerous cells (such as a cavity or void created by removal of the tumor).
Brachytherapy is often divided into two categories: high dose rate (HDR); and low dose rate (LDR). In HDR brachytherapy, a high activity radiation source is placed into the target tissue, often via a previously implanted catheter, for a short period of time, e.g., seconds to a few minutes. In contrast, LDR brachytherapy places a low activity radiation source into the target tissue for a longer, sometimes indefinite, period of time.
Both forms of brachytherapy have advantages. For instance, HDR brachytherapy provides higher radiation levels delivered over a shorter dose delivery period. LDR brachytherapy, on the other hand, utilizes lower activity radiation sources. The energy field of the LDR radiation source results in a measured and localized dose of radiation delivered to the target tissue, e.g., the tumor, gland, or other surrounding tissue. However, the energy field thereafter decays to avoid excessive exposure of nearby healthy tissue.
Due in part to the lower activity of LDR radiation sources, LDR brachytherapy may provide various advantages. For example, for healthcare workers, exposure precautions for LDR brachytherapy may be less stringent than those for HDR brachytherapy. Also there are radiobiological advantages of LDR brachytherapy over HDR brachytherapy (e.g. the dose rate effect) which can lead to better sparing of normal tissue during treatment. Moreover, for patients, the relatively longer implantation period associated with LDR brachytherapy may result in fewer visits to a healthcare facility over the course of radiation treatment, as compared to HDR brachytherapy where patients must return to the healthcare facility for each fraction of radiation delivered for breast brachytherapy, typically 8-10 fractions).
Common radiation sources used in LDR brachytherapy include radioactive isotopes such as Palladium (Pd)-103, Iodine (I)-125, Gold (Au)-198, and Iridium (Ir)-192. While the size and shape of the isotopes may vary, they are, in common applications (e.g., prostate brachytherapy), provided in a standardized size of cylindrically shaped capsules that are approximately the size of a grain of rice, e.g., about 0.8 millimeters (mm) in diameter and about 4.5 mm in length, and are often referred to as “seeds.”
LDR seeds are often delivered through needles using a guide template. The guide template may include a matrix of holes that guide the longitudinal advancement of the needles to insure their proper position relative to the target tissue. Once the needles are properly located in the target tissue, the seeds may be deposited along the longitudinal axis of each needle, after which the needles may be withdrawn.
While effective, current brachytherapy implementations have potential drawbacks. For example, the LDR seeds are typically left indwelling and free floating within the target tissue and are, therefore, susceptible to migration. Moreover, once implanted, LDR seeds are generally not considered to be removable or repositionable. LDR brachytherapy may also require careful dose distribution calculations and seed mapping prior to, and often during, seed implantation. Such calculation and mapping allows effective radiation delivery to the target tissue volume, while minimizing radiation to surrounding healthy tissue (the urethra and rectum, for example, in prostate brachytherapy). Yet, while such dose calculation and seed mapping techniques are effective, problems—such as potentially significant variability in accuracy of seed placement among different clinicians—may exist.
Yet another issue with conventional LDR brachytherapy techniques is that many of these techniques often require the radioactive seeds to be manipulated individually at the time of implantation, an often time-consuming process. Moreover, conventional LDR delivery needles are generally limited to delivering the seeds linearly (along a relatively straight line). Thus, to achieve the desired therapy profile, numerous implants (e.g., about 50-100 seeds are common with prostate brachytherapy), in conjunction with potentially complex dose distribution and mapping techniques and equipment, are often required.